The central hypothesis of Project 2, Energy Balance and Metabolism, is that dietary restriction (DR)[unreadable] increases longevity through changes in energy and substrate metabolism. DR is the only known[unreadable] environmental intervention that consistently increases life span. Because there is a striking relationship[unreadable] between the level of caloric restriction and the magnitude of life extension in rodents, the study of energy[unreadable] metabolism is a fundamental pursuit for probing the actions of DR in primates. Accordingly, we propose to[unreadable] continue our pursuits in this area and have identified the following specific aims. These are to characterize[unreadable] the independent and interactive effects of age and DR on:[unreadable] 1. Body composition to the finest level resolvable;[unreadable] 2. Multiple facets of substrate metabolism, including energy expenditure and glucose homeostasis.[unreadable] effects of body composition on these outcomes will also be evaluated;[unreadable] 3. The bioactivity of adipose tissue.[unreadable] To date, we have documented significant reductions in chronic disease risk factors including decreased[unreadable] obesity, maintenance of fat-free mass, improved insulin sensitivity, and absence of type 2 diabetes.[unreadable] During the coming five years, we will utilize the PPG animals to test the general hypotheses that DR will[unreadable] increase health span and, eventually life span, as displayed by reduced fat mass and metabolic rate, and[unreadable] maintenance of fat-free mass, skeletal muscle mass, and insulin sensitivity. A linking hypothesis is that the[unreadable] effects of DR will be mediated through changes in adipose tissue signals.